Fate map and morphogenesis of presumptive neural crest and dorsal neural tube

In contrast to the classical assumption that neural crest cells are induced in chick as the neural folds elevate, recent data suggest that they are already specified during gastrulation. This prompted us to map the origin of the neural crest and dorsal neural tube in the early avian embryo. Using a combination of focal dye injections and time-lapse imaging, we find that neural crest and dorsal neural tube precursors are present in a broad, crescent-shaped region of the gastrula. Surprisingly, static fate maps together with dynamic confocal imaging reveal that the neural plate border is considerably broader and extends more caudally than expected. Interestingly, we find that the position of the presumptive neural crest broadly correlates with the BMP4 expression domain from gastrula to neurula stages. Some degree of rostrocaudal patterning, albeit incomplete, is already evident in the gastrula. Time-lapse imaging studies show that the neural crest and dorsal neural tube precursors undergo choreographed movements that follow a spatiotemporal progression and include convergence and extension, reorientation, cell intermixing, and motility deep within the embryo. Through these rearrangement and reorganization movements, the neural crest and dorsal neural tube precursors become regionally segregated, coming to occupy predictable rostrocaudal positions along the embryonic axis. This regionalization occurs progressively and appears to be complete in the neurula by stage 7 at levels rostral to Hensen's node.     

Dopamine Inhibits Forskolin- and 3-Isobutyl-1-Methylxanthine-Induced Dark-Adaptive Retinomotor Movements in Isolated Teleost Retinas

We have been investigating the mechanisms of diurnal and circadian regulation of teleost retinomotor movements. In the retinas of lower vertebrates, photoreceptors and melanin pigment granules of the retinal pigment epithelium (RPE) undergo movements at dawn and dusk. These movements continue to occur at subjective dawn and dusk in animals maintained in constant darkness. Cone myoids contract at dawn and elongate at dusk; RPE pigment disperses into the epithelial cells' long apical processes at dawn and aggregates into the cell bodies at dusk. We report here that forskolin, an adenylate cyclase activator, and 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, each induces dark-adaptive cone and RPE retinomotor movements in isolated light-adapted green sunfish retinas cultured in constant light. Forskolin induces a 22-fold elevation in retinal cyclic AMP content. Forskolin- and IBMX-induced movements are inhibited approximately 65% and 95%, respectively, by 3,4-dihydroxyphenylethylamine (dopamine). However, dopamine does not inhibit dark-adaptive movements induced by dibutyryl cyclic AMP. Epinephrine is much less effective than dopamine in inhibiting forskolin-induced movements, while phenylephrine and clonidine are totally ineffective. These results are consistent with our previous findings that treatments that increase intracellular cyclic AMP content promote dark-adaptive retinomotor movement. They further suggest that dopamine inhibits adenylate cyclase activity in photoreceptors and RPE cells and thereby favors light-adaptive retinomotor movements.     

Movement patterns of an Australian chrysomelid beetle in a stand of two Eucalyptus host species

Summary We examined the movements of Chrysophtharta hectica, a eucalypt-feeding chrysomelid beetle in New South Wales, Australia, in relation to the beetle's sex, age and life-history, and to attributes of its Eucalyptus host plants. Beetle movements within the site were not influenced by beetle age or sex, but may be related to generation. Beetle distributions on the two host plant species, Eucalyptus stellulata and E. pauciflora, were generally clumped. Some of this clumping resulted from preference for E. stellulata over E. pauciflora. Clumping of beetles also occurred within host plant species; some plant individuals were consistently heavily used by beetles over the course of three years. We examined nutritional, spatial and biomass attributes of plants and found plant height and foliage production to be the best predictors of beetle numbers.     

Is Corporate Social Responsibility Oiling the Neoliberal Carbon Economy?

ABSTRACT

This study focuses on the corporate social responsibility (CSR) work the Austrian energy company OMV pursued as it constructed a gas power plant on the shores of the Black Sea. I argue that neither social movement theory nor CSR theory fully explain what happened in this case. Environmental protests quickly became embedded in local politics and national identity figurations, and the CSR work by the company was transformed and domesticated by local actors. While agency and power was thus distributed, various actors also shared a common language, tapping into a globally circulating discourse that has gained traction in Turkey with the current neoliberal policies. The way CSR was played out and negotiated in this case meant that social capital and equity were construed as issues of concern, while environmental issues were downplayed. Thus, in the process, the double bind between the growth economy and ecologies of survival was effectively reproduced.     

Light intensity and schooling behaviour in larval gulf menhaden

Schooling behaviour was examined in larval gulf menhaden Brevoortia patronus under decreasing and increasing light intensities and related to movements of retinal photoreceptors and pigment. Nearest neighbour angles and nearest neighbour distances between fish were inversely related to light intensity and were independent of the direction of intensity change. Swimming speeds of individual fish were directly related to light intensity when intensity was decreased but did not increase when intensity was raised. The changes in nearest neighbour angles and distances more closely paralleled movements of retinal pigment cells than cone cell migration, suggesting that rod photoreceptors play a greater role than cones in determining the threshold light intensity for schooling. A general model is developed relating the threshold light intensity for schooling to eye diameter for a number of different species and the implications of this relationship are discussed.     

Tonic and modulatory subsystems of the complex gravity receptor system in crickets, Gryllus bimaculatus

The gravity receptor system of crickets Gryllus bimaculatus is composed of antennal, cercal and leg subsystems. The cercal gravity receptors are the club-shaped sensilla. Each of these subsystems elicits compensatory head movements during passive roll.The extent of compensatory head movements depends on the strength of the gravitational stimulus applied to the leg subsystem. Amputation of 2 legs never causes a decrease in reflex amplitude. Unilateral amputation of 1 to 3 legs always induces a roll movement of the head to the intact body side. Therefore, the leg gravity receptor system exerts a modulatory and tonic effect on the neck muscles.The gravity receptors of 1 cercus or 1 antenna only elicit compensatory head movements. They exert no tonic effect on the neck muscles.The results are discussed with respect to (i) the proposed connectivity of the cercus-neck muscle pathway, (ii) mutual inhibitory interactions between the sensory pathways originating in the leg gravity receptors, and (iii) the influence of non-gravitationally induced excitation on the occurrence of compensatory head movements during passive roll of the crickets.     

Racialized political shock: Arab American racial formation and the impact of political events

This article explores significant factors influencing the process of Arab American racial formation. I bring into conversation theories of racial formation and ‘political shock’ in social movement scholarship to develop the notion of ‘racialized political shock’ as an important factor in how racial and ethnic groups mobilize and organize. Many moments of political shock are highly racialized and have the potential to reorder the racial and ethnic landscape in ways that can open opportunities or introduce constraints to mobilizations around racial formation. Drawing on existing studies of Arab Americans, this paper highlights how Arab American racial formation has been galvanized during moments of racialized political shock. In the Arab American case, these moments have led to a call for recognition outside the category of white. I conclude by outlining ways forward in the study of Arab Americans, who have been overlooked in studies of race and ethnicity in the US.     

Noninvasive genetic sampling reveals intrasex territoriality in wolverines

Due to its conspicuous manifestations and its capacity to shape the configuration and dynamics of wild populations, territorial behavior has long intrigued ecologists. Territoriality and other animal interactions in situ have traditionally been studied via direct observations and telemetry. Here, we explore whether noninvasive genetic sampling, which is increasingly supplementing traditional field methods in ecological research, can reveal territorial behavior in an elusive carnivore, the wolverine (Gulo gulo). Using the locations of genotyped wolverine scat samples collected annually over a period of 12 years in central Norway, we test three predictions: (1) male home ranges constructed from noninvasive genetic sampling data are larger than those of females, (2) individuals avoid areas used by other conspecifics of the same sex (intrasexual territoriality), and (3) avoidance of same‐sex territories diminishes or disappears after the territory owner's death. Each of these predictions is substantiated by our results: sex‐specific differences in home range size and intrasexual territoriality in wolverine are patently reflected in the spatial and temporal configuration of noninvasively collected genetic samples. Our study confirms that wildlife monitoring programs can utilize the spatial information in noninvasive genetic sampling data to detect and quantify home ranges and social organization.     

Chloroplast translocations induced by light pulses

The effect of single blue-light pulses on chloroplast rearrangement was studied in the leaves of Tradescantia albiflora, Chlorophytum elatum, and Lemna trisulca. For measuring translocations in terrestrial plants the method of transmission changes was used; translocations in the water plant Lemna were studied by direct microscopic observation and counting. Strong light (30 W m^-2) applied in the form of short pulses, shorter than a lag period of translocations, induces some transient effects in the following dark period. With short pulses, transient rearrangements of chloroplasts to a weak-light position were found. With longer pulse duration, biphasic responses took place in Tradescantia and Lemna: The initial movement to a partial strong-light position was followed by a wave of translocation to a weak-light arrangement. In Chlorophytum this type of response appeared only in a narrow fluence range. The validity of the reciprocity law in relation to fluence rate and time of irradiation was confirmed for Tradescantia. The results may give us an insight into the kinetics of the primary effects of light in the translocation process.